GISS Tweaks the Short-Term Global Temperature Trend Upwards

SEE UPDATE 2 AT END OF POST

GISS released its August 2014 global surface temperature data today. As I was preparing the graphs for the August 2014 s4urface and lower troposphere temperature update, I noticed a sizeable jump in the short-term trend in the GISS data. (I’ll try to post the full update this evening.)  The August GISS LOTI value is higher than July, but it should not have had that much of an effect on the trend for the period of January 1998 to present. Not too surprisingly, much of the increase in trend was caused by adjustments to data from 2000 to 2013.

Figure 1 compares the short-term annual trend of two recent versions of the GISS global surface temperature data, from 1998 to 2013. The version as of August 7, 2014 (through June 2014) is available through the Wayback Machine here, and the August 2014 update is available through the GISS website here.

Figure 1

Now keep in mind that we’re not looking at the 2014 data so any variations this year do not impact these trends. In June 2014, the 1998-2013 trend was 0.062 deg C/decade, and a few months later, it jumped up to 0.066 deg C/decade.

The old short-term trend must not have been high enough. GISS must not like it that the UKMO’s HADCRUT4 data is catching up with them during this period.  Can’t have that.

It has been said before.  It will be said again.  The adjustments always seem to add to global warming.

PS: Yes, I realize we’re discussing a trends presented in thousandths of a deg C/decade. But these small changes keep coming and they add up.

UPDATE (September 15, 2014):  Sorry, I should’ve included a graph with the year-to-date (January to June) 2014 data to also show the impacts of the tweaks on this year. See Figure 2.

Figure 2

With the adjustments, 2014 has a better chance of matching or breaking records.

That explains it.

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UPDATE 2 (September 16, 2014):  Animation 1 compares GISS trend maps.  One was downloaded on June 12, 2014.  The second was downloaded yesterday June 15, 2014. To complicate the comparison, GISS recently revised their Robinson projection maps. On their Updates to Analysis webpage, they write:

September 15, 2014: Color maps using the Robinson projection are now presented without contour smoothing, since that process occasionally results in skipping some color bands.

It appears, however, that there is new data in the Arctic, north of eastern Siberia. GISS must’ve found an island in the Arctic Ocean with some data so they could infill that region with missing data.

Animation 1